Do you have a friend who can eat whatever she wants and however much of it, yet never gain weight? And do you work hard to control your diet and exercise, and still struggle to keep off the weight? Life can seem unfair! That's why it's important to know that genetics are a huge component of body shape and build. They also determine how our bodies burn calories and build muscles. While there is not much you can do about your genes, you can try to find a diet and exercise program which is best suited for your body. What allows your friend to keep in shape, may be very different from what your body needs. Also try to focus on those things you can change, that is increasing your metabolic rate and adopting healthy eating and exercise habits that you can sustain.